Achieving accurate, real-time measurements during well completion and stimulation treatments has long been a goal in the oil and gas industry. Accurate measurement of bottom hole pressure during fracture treatments, for example, would allow an operator to observe fracture growth trends in real-time, and change treatment conditions accordingly. Similarly, measurement of ball location would facilitate acid bailout treatments. However, real-time measurements of borehole completion and stimulation treatments are rarely performed with current technology because the borehole environment is hostile to wiring and tends to rapidly attenuate electromagnetic signals. For example, the abrasiveness of the fracturing slurry is destructive to any exposed cable placed in the wellbore for delivering data to the surface.
Techniques for providing real-time measurements during drilling operations are known. For example, formation properties may be measured during the excavation of the borehole, or shortly thereafter, through the use of tools integrated into the bottomhole assembly (“BHA”). Logging while drilling has the advantage of measuring properties of a formation before drilling fluids invade deeply. However, many wellbores prove to be difficult or even impossible to measure with conventional wireline tools, especially highly deviated wells. Consequently, when drilling operations have ended and the BHA is withdrawn from the borehole, e.g., in the completion phase or during stimulation treatments, it is often impractical to obtain real-time measurements.
One attempt to deliver bottom hole pressure measurement data in real-time is described in Doublet, L. E., Nevans, J. W., Fisher, M. K., Heine, R. L, Blasingame, T. A., Pressure Transient Data Acquisition and Analysis Using Real Time Electromagnetic Telemetry, SPE 35161, March 1996 (“Doublet”). Doublet teaches that pressure measurements are transmitted from a downhole gauge to the surface through the formation strata via electromagnetic signals. Although this technique has been used successfully on some wells, it is limited by the well depth and the types of rock layers through which a signal could be transmitted clearly. In particular, electromagnetic signals are rapidly attenuated by the formation. These limitations render the technique impractical for use in many wells, and particularly in deep wells.
Gathering data from the region of a formation between boreholes is also known. Typically, a seismic source in one borehole creates waves which are detected in another borehole. Formation properties may be calculated from attenuation, dispersion and travel time of the waves between the boreholes. An implosive device might be utilized as the seismic source. For example, imploding spheres and other shapes have been used as underwater acoustic sources for ocean applications as described in Heard, G. J., McDonald, M., Chapman, N. R., Jashke, L., “Underwater light bulb implosions—a useful acoustic source,” Proc IEEE Oceans '97; M. Orr and M. Schoenberg, “Acoustic signatures from deep water implosions of spherical cavities,” J. Acoustic Society Am., 59, 1155-1159, 1976; R. J. Urick, “Implosions as Sources of Underwater Sound,” J. Acoustic Society Am, 35, 2026-2027, 1963; and Giotto, A., and Penrose, J. D., “Investigating the acoustic properties of the underwater implosions of light globes and evacuated spheres,” Australian Acoustical Society Conference, Nov. 15-17, 2000. A device with a vacuum or low pressure chamber which is released into the water to sink will eventually implode when the hydrostatic pressure exceeds the implosion threshold of the device. A triggering mechanism may even be used to cause the device to implode before pressure alone would do so as described in Harben, P. E., Boro, C., Dorman, Pulli, J., 2000, “Use of imploding spheres: an Alternative to Explosives as Acoustic Sources at mid-Latitude SOFAR Channel Depths,” Lawrence Livermore National Laboratory Report, UCRL-ID-139032. One example of an implosive device is commercial light bulbs, as described in both Heard, G. J., McDonald, M., Chapman, N. R., Jashke, L., “Underwater light bulb implosions—a useful acoustic source,” Proc IEEE Oceans '97; and Giotto. The controlled use of implosive sources in a wellbore is described in U.S. Pat. No. 4,805,726 of Taylor, D. T., Brooks, J. E., titled “Controlled Implosive Downhole Seismic Source.”